Intake Air Temperature (IAT) Sensor

The two-wire Intake Manifold Air Temperature (IAT) sensor is installed in the intake manifold with the sensor element extending into the air stream.

This is a Negative Thermal Coefficient (NTC), meaning that as the manifold air temperature increases, the resistance (voltage) in the sensor decreases, and vice-versa.

The IAT sensor provides an input voltage to the PCM, indicating the density of the air entering the intake manifold based on intake manifold air temperature. When the ignition is turned
ON
, a 5-volt power circuit is supplied to the sensor from the PCM. The sensor is grounded at the PCM through a low-noise, sensor-return circuit.

The PCM uses this input to determine:

Injector pulse-width (air: fuel ratio)

Ignition timing (to prevent spark knock)

Fig. IAT sensor installed in the intake manifold of a 5.2L engine. Others similar

TESTING

Be sure the ignition is
OFF
.

Disconnect the connector at the IAT sensor.

Check resistance across the sensor terminals. Using an input impedance (digital) VOM is recommended.

Resistance will vary with temperature, but should be about 18 kilo-ohms at 50ºF (10ºC), decreasing rapidly as temperature increases to about 1kilo-ohms at 176ºF (80ºC) which is near engine operating temperature. If the measured resistance is at or near zero (shorted) or at or near infinity (open), replace the sensor.

To test the harness, proceed as follows:

Shut the ignition
OFF
and disconnect the battery negative cable.

Unplug the PCM, test the harness between the proper PCM connector terminal and the sensor connector. Also check the harness between the proper PCM connector terminal and the sensor connector. If resistance is more than 1 ohm, repair the wiring harness.

WARNING

Testing the wiring harness with the PCM still connected can cause serious damage to the processor. ALWAYS disconnect the PCM before testing the wiring harness, unless instructed otherwise.

Connect the negative battery cable.

Fig. Testing the IAT sensor with an ohmmeter connected across the two sensor terminals